The present invention relates to antennas generally and more particularly to dipole antennas.
The following U.S. patents are believed to represent the current state of the art:
U.S. Pat. Nos. 4,748,450; 5,079,562; 5,311,201; 6,215,451 and 6,421,024.
The present invention seeks to provide a cost effective multi-band sleeve dipole antenna.
There is thus provided in accordance with a preferred embodiment of the present invention a multi-band sleeve dipole antenna including a generally axially disposed elongate inner conductor having first and second ends and arranged to be connected at the first end thereof to a modulated signal source, a generally axially disposed intermediate conductor disposed generally coaxially with respect to the inner conductor and arranged to be connected to ground, a generally axially disposed first outer sleeve conductor disposed generally coaxially with respect to the inner conductor and to the intermediate conductor and a generally axially disposed second outer sleeve conductor having a first and second ends disposed generally coaxially with respect to the inner conductor and to the intermediate conductor, the first end being adjacent and axially separated from the first outer sleeve conductor by an axial gap, the first outer sleeve conductor being electrically connected to the intermediate conductor at a feed point location along the inner conductor which is axially separated from the second end thereof by a distance generally equal to one-quarter wavelength of a first radio transmission frequency, the first outer sleeve conductor extending beyond the feed point location by a distance generally equal to one-quarter wavelength of a second radio transmission frequency, which is higher than the first radio transmission frequency, the second outer sleeve conductor being electrically connected to the inner conductor at a location at the second end of the second outer sleeve conductor, and the first end of the second outer sleeve conductor being axially separated from the second end of the inner conductor by a distance equal to one-half wavelength of the second radio transmission frequency.
In accordance with another preferred embodiment of the present invention an inner diameter of the first outer sleeve conductor is selected to define an impedance between the first outer sleeve conductor and the intermediate conductor which is selected to maximize operating bandwidth. Alternatively or additionally, an inner diameter of the second outer sleeve conductor is selected to define an impedance between the second outer sleeve conductor and the inner conductor which is selected to maximize operating bandwidth.
Preferably, the axial gap is selected to provide approximate coupling between the first outer sleeve conductor and the second outer sleeve conductor.
In accordance with still another preferred embodiment of the present invention the multi-band sleeve dipole antenna also includes a coaxial connector having a center pin electrically connected to the inner conductor and an outer connector conductor electrically connected to the intermediate conductor.
Preferably, the second outer sleeve conductor is not electrically connected to the inner conductor at the first end of the second outer sleeve conductor. Additionally or alternatively, the first outer sleeve conductor is not electrically connected to the inner conductor or to the intermediate conductor at an end of the first outer sleeve conductor adjacent the axial gap.
In accordance with a preferred embodiment of the present invention the first and second radio transmission frequencies are generally in the 800 MHz and 1900 MHz bands. Alternatively, the first and second radio transmission frequencies are generally in the 2.4 GHz and 5.6 GHz bands.
There is also provided in accordance with another preferred embodiment of the present invention a multi-band sleeve dipole antenna including a generally axially disposed elongate inner conductor having first and second ends and arranged to be connected at the first end thereof to a modulated signal source, a generally axially disposed intermediate conductor disposed generally coaxially with respect to the inner conductor and arranged to be connected to ground, a generally axially disposed first outer sleeve conductor disposed generally coaxially with respect to the inner conductor and to the intermediate conductor and a generally axially disposed second outer sleeve conductor having a first and second ends disposed generally coaxially with respect to the inner conductor and to the intermediate conductor, the first end being adjacent and axially separated from the first outer sleeve conductor by an axial gap, dimensions and electrical interconnections between the inner conductor, intermediate conductor and first and second outer sleeve conductors being selected so as to provide dipole performance in first and second radio transmission bands.
Preferably, the first and second radio transmission bands are generally in the range of 800 MHz and 1900 MHz. Alternatively, the first and second radio transmission bands are generally in the range of 2.4 GHz and 5.6 GHz.